EMPLACEMENT AGES OF KIMBERLITE OCCURRENCES IN THE PRIESKA REGION, SOUTHWEST BORDER OF THE KAAPVAAL CRATON, SOUTH-AFRICA

Rb-Sr (mica) and U-Pb (perovskite) emplacement ages for kimberlites fr om the southwest part of the Kaapvaal Craton, near Prieska, South Afri ca, vary from as old as 170 Ma to as young as 74 Ma, similar to ages e lsewhere in southern Africa. Isotopically defined Group-I and -II kimb erlites are found on the Kaapvaal Craton northeast of the Doomberg and Brakbos lineaments (Domains I and II as defined by Skinner et al., 19 92), with ages of 74, 108 and 118-125 Ma. Kimberlites in the craton ma rgin area bounded by the two lineaments (Domain III) are exclusively G roup II, with ages of 116-119 Ma. Kimberlites in Domain IV, to the sou th of the craton boundary, are of Group-I affinity emplaced in two epi sodes at 74 and 100-103 Ma. Southernmost Domain V is dominated by kimb erlites petrographically, chemically and isotopically transitional bet ween Group-I and -II types, but with the oldest ages at 140 and possib ly 170 Ma. Phlogopite from a peridotite xenolith from the Sanddrift ki mberlite has retained an age of 2250 Ma, presumably the enrichment age of the nodule.